The present invention relates to a process for producing menaquinone-4 (referred to as MK-4 hereinafter) represented by the following formula: ##STR1## MK-4 is vitamin K.sub.2 -4 taking part in blood coagulation and control of calcium metabolism of a living body.
Menaquinones contained in bacteria have been thoroughly studied from the taxonomical viewpoint, and summarized by M. D. Collins and D. Jones (Microbiol. Rev., 45: 316-354, 1981). However bacteria containing a considerable amount of MK-4 as the main menaquinone have not been found. Recently, production of MK-4 by Flavobacterium meningosepticum as a Gram-negative bacterium has been reported by Tani et al (J. Ferment. Technol., 62: 321-327, 1984).
Improvement in industrial production of MK-4 has been required. The present inventors have studied about production of MK-4 by fermentation of microorganisms and have found microorganisms capable of producing MK-4 in good yield other than Flavobacterium meningosepticum.